Add container attach support.

Signed-off-by: Lantao Liu <lantaol@google.com>

pkg/ioutil/write_closer.go

@@ -0,0 +1,68 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package ioutil
+
+import "io"
+
+// writeCloseInformer wraps passed in write closer with a close channel.
+// Caller could wait on the close channel for the write closer to be
+// closed.
+type writeCloseInformer struct {
+	close chan struct{}
+	wc    io.WriteCloser
+}
+
+// NewWriteCloseInformer creates the writeCloseInformer from a write closer.
+func NewWriteCloseInformer(wc io.WriteCloser) (io.WriteCloser, <-chan struct{}) {
+	close := make(chan struct{})
+	return &writeCloseInformer{
+		close: close,
+		wc:    wc,
+	}, close
+}
+
+// Write passes through the data into the internal write closer.
+func (w *writeCloseInformer) Write(p []byte) (int, error) {
+	return w.wc.Write(p)
+}
+
+// Close closes the internal write closer and inform the close channel.
+func (w *writeCloseInformer) Close() error {
+	err := w.wc.Close()
+	close(w.close)
+	return err
+}
+
+// nopWriteCloser wraps passed in writer with a nop close function.
+type nopWriteCloser struct {
+	w io.Writer
+}
+
+// NewNopWriteCloser creates the nopWriteCloser from a writer.
+func NewNopWriteCloser(w io.Writer) io.WriteCloser {
+	return &nopWriteCloser{w: w}
+}
+
+// Write passes through the data into the internal writer.
+func (n *nopWriteCloser) Write(p []byte) (int, error) {
+	return n.w.Write(p)
+}
+
+// Close is a nop close function.
+func (n *nopWriteCloser) Close() error {
+	return nil
+}